The technology of CCD image sensors constantly improves leading to increasing image sensor resolutions. Today, high performance cameras are equipped with 10-20 Mega pixel resolution sensors or even higher resolutions. Low performance cameras in mobile phones use 3 mega pixel sensors or even higher resolutions. Future high and low performance cameras will most likely follow the trend of using image sensors with even higher pixel resolutions.
The increasing pixel resolution provides increasing amounts of image data to be processed and transferred from one device to another, for example from the mobile phone to a computer or the Internet. Accordingly, data processors and electronic memory must meet higher speed and capacity requirements in order to handle the increasing amounts of image data.
Cameras may be used both for still picture recording and video recording. Video recording typically requires lower pixel resolution than the nominal sensor resolution in order meet requirements of readout speed and memory capacity for video images. Accordingly, the resolution of the image sensor needs to be downscaled for video recording.
Another problem related to the increasing pixel resolutions of image sensors is related to the sensor's sensitivity to light and the dynamic range of sensor. In order to increase the image sensor's sensitivity to light, for example under low light level conditions, the pixel resolution of the image sensor may beneficially be reduced by binning together a number of pixels. By binning together a number of pixels the light receiving area of one pixel increases and consequently, also the light sensitivity of the sensor increases.
The amount of image data generated by an image sensor can be reduced by reading out only a fraction of pixels from the image sensor, for example by reading out only every second or third pixel and skipping the rest. However such method results in poor image quality.
Accordingly it may be seen as a problem to reduce the amount of image data without reducing the image quality significantly.
US 2006/0203113 discloses a method for downsizing pixel information by pixel binning. An example describes that four (2×2) pixels are skipped and added and an amount of pixel information is compressed at a ratio of ¼. First, all pieces of pixel information of a same colour filter in first and third columns of a first row and the first and the third column of a third row, all pieces of pixel information of G in this example, are added and outputted as information for one pixel. Next, all pieces of pixel information of a same colour filter in second and fourth columns of the first row and the second and the fourth columns of the third row, all pieces of pixel information of B in this example, are added and outputted as information for one pixel. Then, all pieces of pixel information in fifth and seventh columns of the first row and the fifth and the seventh columns of the third row, all pieces of pixel information of G in this example, are added and outputted as information for one pixel. When the same operation is repeated and pixels to be read out reach a last column or a column near the last column, then all pieces of pixel information of a same colour filter in the first and the third columns of a second row and the first and the third columns of a fourth row, all pieces of pixel information of R in this example, are added and outputted as information for one pixel.